The present invention relates to a solenoid valve, more particularly to a proportional hydraulic valve, which is installed within a hydraulic system of a device for varying valve timing of gas exchange valves In an Internal combustion engine, said solenoid valve generally comprising:
an electromagnet having a magnet housing, at least one coil winding, an armature, a first pole shoe and a second pole shoe,
and a valve member having a hollow cylindrical valve housing for receiving a spool valve that is displaceable relative to the valve housing by the armature of the electromagnet.
A generic solenoid valve of the pre-cited type is known from DE 4 228 045 A1. This solenoid valve generally comprises an electromagnet having a hollow cylindrical magnet housing, a coil winding, an armature, a first and a second pole shoe, and further comprising a valve member having a likewise hollow cylindrical valve housing for receiving a spool valve that Is displaceable relative to the valve housing by the armature of the electromagnet. The connection between the electromagnet and the valve member is effected with the help of a bottom of the magnet housing adjacent the valve member. This bottom has a central aperture into which a flange of the valve housing is introduced so that the valve housing is suspended from the magnet housing to project outwards therefrom, The valve member is then force-locked and positively engaged with the bottom of the magnet housing by a first pole shoe which is mounted in the magnet housing and by the coil winding, the second pole shoe and a cap of the electromagnet.
Another possibility of connecting the electromagnet and the valve member of a solenoid valve is known from DE 4 423 122 A1. In this solenoid valve, which is basically made up of the same elements the valve housing likewise comprises a flange which bears against a pole shoe of the electromagnet that at the same time constitutes the bottom of the magnet housing. For fixing the valve member on the electromagnet, the magnet housing of the electromagnet has an extension whose edge portion adjacent the valve member is bent round to surround the flange of the valve housing so that the valve member is likewise fixed on the electromagnet by force-locking and positive engagement.
The drawings of EP 0 212 458 further disclose that in a solenoid valve, the bottom of the magnet housing of the electromagnet has a hollow cylindrical extension coaxial to the valve member, and the outer peripheral surface of this extension comprises a thread. The valve housing of the valve member in this solution likewise comprises a flange. A union nut is slipped onto the valve housing and supported on this flange and then screwed onto the extension of the magnet housing of the electromagnet so that the valve member is force-locked to the electromagnet.
A drawback of these prior art solenoid valves is that the connections between the electromagnets and the valve members are relatively complicated to manufacture and cost-intensive and do not effect an adequate radial fixing for assuring the required exact alignment between the bore of the valve housing for receiving the spool valve and the armature of the electromagnet. Additionally, these prior art connections between the electromagnet and the valve member are not stable enough to exclude the danger of detrimental effects on the bore of the valve housing for the spool valve during assembly and operation of the solenoid valve. Moreover, these connections are often subjected to considerable loads which, in the case of less stable connections, cause a loosening or a disengagement of the valve member from the electromagnet, and the resulting axial offset between the bore for the spool valve and the armature of the electromagnet leads to a failure of the solenoid valve. Further, if the connection between the electromagnet and the valve member of the solenoid valve is too tight, the high forces of assembly can cause deformation Of the bore for the spool valve In the valve housing which can lead to a binding of the spool valve in the bore and, thus also, to a failure of the solenoid valve.
It is therefore an object of the invention to provide a solenoid valve, more particularly a proportional hydraulic valve, in which the connection between the electromagnet and the valve member is characterized by low manufacturing and assembly costs while, at the same time, offering good facilities for a radial fixing of the valve member on the electromagnet.
Another object of the invention is to exclude detrimental effects on the bore for the spool valve in the valve housing during assembly and operation of the solenoid valve to the greatest possible extent.
These and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that the electromagnet and the valve member are connected and fixed radially and axially to each other by force-locking and/or positive engagement with the help of the second pole shoe of the electromagnet that is arranged adjacent the valve member and is configured as a plug-in lock for the valve housing.
According to one advantageous feature of the Invention, the second pole shoe of the electromagnet comprises, adjacent the valve member, a preferably hollow cylindrical, coaxial extension which is configured on the inside as a plug-in lock for the valve housing of the valve member and is thin-walled at least in its free, circumferential edge portion. Such a plugged connection enables an exact radial fixing of the entire valve member before it is connected to the electromagnet, to that the required exact alignment of the bare for the spool valve In the housing to the armature of the electromagnet is assured.
In a particularly advantageous first embodiment of the connection of the electromagnet to the valve member, an end region of the valve member adjacent the electromagnet preferably comprises a circumferential annular groove and the electromagnet Is connected to the valve member by a toothed clamping-In of the thin-walled edge portion of the extension of the second pole shoe into this annular groove. For this purpose, a toothed matrix having a diameter of a dimension between the outer diameter of the valve housing and the outer diameter of the thin-welled edge portion of the extension of the second pole shoe is moved in axial or radial direction over the valve housing toward the electromagnet. When the matrix strikes the thin-walled edge portion of the extension of the second pole shoe, this edge portion is pressed into the circumferential annular groove arranged in the end region of the valve housing. At the same time, the valve housing is pressed against a support surface in the extension of the second pole shoe so that, upon an unloading of the parts concerned, the pole shoe and the valve housing are braced axially against each other, Due to the toothing of the crimped connection, the thin-walled edge portion of the extension of the pole shoe is pressed deeper into the annular groove of the valve housing in tho region of the teeth than in the region of the gaps between the teeth so that the valve member is prevented at the same time from rotating relative to the electromagnet. As an alternative to this connection with the help of a crimping matrix, a similar connection between the electromagnet and the valve member can also be made by press crimping.
In an equally advantageous second embodiment of the connection of the electromagnet to the valve member, an end region of the valve housing adjacent the electromagnet is configured preferably with two circumferential annular grooves and the edge portion of the extension of the second pole shoe is rolled Into these annular grooves thus connecting the electromagnet to the valve member. For this purpose, the thin-walled edge portion of the extension of the pole shoe of the electromagnet is pressed into the annular grooves of the valve housing by a shaping tool during a rotary motion of the electromagnet and the valve member, or also of the shaping tool. In this embodiment, too, the valve housing is pressed at the same time against a support surface in the extension of the pole shoe so that after the unloading of the parts concerned, the pole shoe and the valve housing are braced axially against each other. A separate anti-rotation device between the valve member and the electromagnet has proved to be unnecessary In this type of connection because the double pressing of the edge portion of the extension of the pole shoe into the two annular grooves of the valve housing results in a force-locking that effectively prevents rotation. The arrangement of two annular grooves on the valve housing, however, Is only one preferred embodiment and does not exclude the provision of more or less than two annular grooves and the resulting multiple or single rolled-in connection between the electromagnet and the valve member.
Finally, in a third advantageous embodiment of the connection of the electromagnet to the valve member, the valve housing Is configured preferably with a plurality of cavities in an end region adjacent the electromagnet, and the electromagnet is connected to the valve member by a localized swaging of the edge portion of the extension of the second pole shoe Into these cavities. These cavities may be made as radial pocket or through-bores in the valve housing in any desired number and may be arranged symmetrically or asymmetrically in one or more circumferential lines around the periphery of the end region of the valve housing adjacent the electromagnet. The thin-walled edge portion of the extension of second pole shoe is then pressed with the help of a die at appropriate points into these cavities in the valve housing, while the valve housing is pressed at the same time against a support surface in the extension of the pole shoe. Thus, after the unloading of the parts concerned, both an axial bracing between the pole shoe and the valve housing and a prevention of rotation of the valve member relative to the electromagnet are obtained. A similar connection of the valve member to the electromagnet can be made in a modified form of this embodiment in which the edge portion of the extension of the second pole shoe is swaged to the valve housing without the provision of separate cavities in the valve housing.
The solenoid valve of the invention, particularly a proportional hydraulic valve, has the advantage, in all its proposed embodiments, over the prior art solenoid valves that the connection between the electromagnet and the valve member can be established by a simple chipless shaping of the thin-walled edge portion of the coaxial extension of the pole shoe situated adjacent the valve member. Since, in addition, this pole shoe can be made as a low-cost extrusion molded part the connection of the invention is characterized in that it has the lowest possible manufacturing and assembly costs as well as optimum strength properties. At the same time, due to the plug-in lock configured on the inner side of the extension of the pole shoe adjacent the valve member, an advantageous possibility of a radial fixing of the valve member on the electromagnet is created 8o that detrimental effects on the reception bore for the spool valve in the valve housing during assembly and operation of the solenoid valve are largely excluded. A further advantage of the solenoid valve of the invention, finally, is that, due to the type of connection between the electromagnet and the valve member, the hitherto mostly required fixing shoulder of enlarged diameter on the valve housing can now be omitted, so that the valve housing, too, can be manufactured economically with a continuous outer diameter.
The invention will now be described more closely with reference to a few examples of embodiment represented in the appended drawings.